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Stemborer attack in maize, sorghum and millet in Africa causes annual average losses of 15-20%. Several species are responsible including the introduced Chilo partellus, which was first noted in Africa in the 1930s. Originally from the Indian...

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Stemborer attack in maize, sorghum and millet in Africa causes annual average losses of 15-20%. Several species are responsible including the introduced Chilo partellus, which was first noted in Africa in the 1930s. Originally from the Indian sub-continent, Chilo partellus is now the most damaging species at mid-to-lower elevations in East Africa.
To overcome the difficulties, even impracticalities, of control using agrochemicals (the borer spends much of its life burrowing in the stem out of reach of pesticides, which few farmers can afford anyway) the International Centre of Insect Physiology and Ecology (ICIPE) has been pursuing the alternative option of biological control.
In 1991, ICIPE and the International Institute for Biological Control (IIBC) in Pakistan identified a promising predator, a small parasitic wasp, Cotesia flavipes. The wasp follows the stem borer into the stem and there injects it with 40-50 eggs: when the larvae hatch, they consume the pest. Two years of laboratory studies in Kenya established that the predator attacked only stem borers and that it attacked two native borers in addition to Chilo partellus. Cotesia flavipes was then released at three sites in the coastal region of Kenya in 1993 and monitoring has shown that the number of borers attacked by C. flavipes has increased year on year. In India and Pakistan, the average rate of parasitism by C. flavipes is 30-40% and, if that level can be achieved in Kenya, it will have proved an economically viable control method.
Although Chilo partellus has not yet reached West Africa, it is still spreading and there are no obvious barriers to prevent it crossing the continent. To anticipate this eventuality, ICIPE is working with LITO to test East African predators against borers native to West Africa. In addition they are making test releases of Cotesia flavipes in Nigeria to assess its ability to survive, spread and parasitize local stem borer species.
[caption to illustration]
Stemborers the cause of significant losses in maize and sorghum
Dr W Overholt, ICIPE
PO Box 30772, Nairobi, KENYA